RF Digital Predistortion Using Baseband-Derived Coefficients
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Solution Overview
Problem
Existing power amplifier linearization techniques, such as digital baseband predistortion, require wideband transmit paths and additional components like envelope detectors and RF delay lines, leading to increased cost, complexity, and inaccuracy, while RF envelope digital predistortion suffers from inaccuracy and loss.
Innovation Solution
A new predistortion system architecture that applies a predistortion function derived at baseband to RF, using a vector modulator and a digital delay to compensate for delay mismatch, with correction coefficients obtained from a lookup table or polynomial calculation, reducing the need for wideband components and improving linearization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital baseband predistortion is implemented, then linearization performance is improved, but the transmit path bandwidth requirement increases several times beyond signal bandwidth
Solution Approach 1:
The patent transitions from baseband predistortion to RF predistortion, changing the operational dimension from baseband to RF frequency domain. This allows the predistortion function to be applied at the RF stage rather than requiring wideband baseband processing, thereby reducing the transmit path bandwidth requirement while maintaining linearization performance.
Solution Approach 2:
The patent extracts the predistortion function application point from the baseband stage and relocates it to the RF stage. By separating the predistortion function derivation (done at baseband) from its application (done at RF), the system avoids the need for wideband baseband components while achieving the same linearization effect.
2Area of stationary object
If RF envelope digital predistortion is used, then transmit path bandwidth requirement is reduced, but additional components like envelope detectors and RF delay lines increase cost and complexity
Solution Approach 1:
The patent merges the predistortion function application with the existing RF signal path by applying it directly to the complex RF signal. This eliminates the need for separate envelope detection and RF delay line components that would be required by traditional RF envelope predistortion, as the complex signal processing inherently handles both magnitude and phase information.
Solution Approach 2:
The patent uses a universal complex signal processing approach that handles both amplitude and phase predistortion simultaneously. This multi-functional approach replaces the need for separate envelope detection, phase detection, and delay compensation components, reducing overall system complexity while maintaining the ability to compensate for RF power amplifier nonlinearities.
3Area of stationary object
If RF envelope digital predistortion components are added, then transmit path bandwidth is reduced, but measurement precision and accuracy decrease due to additional components
Solution Approach 1:
The patent uses digital signal processing to create a precise mathematical model (copy) of the RF power amplifier's nonlinear behavior. By deriving the predistortion function digitally from measured amplifier characteristics and applying it through complex signal processing, the system achieves high measurement precision without the signal degradation that would result from analog envelope detectors and RF delay lines.
Data Source
AI summary
A baseband-derived RF predistortion system using a lookup table having coefficients extracted at baseband and then applied at RF by means of a vector modulator. The architecture combines the narrowband advantage of envelope predistortion with the accuracy of baseband predistortion, and including compensation for memory effects. A polynomial-based alternative is also described.